- Email: [email protected]
Electromagnetic and microwave absorption properties of BaMgxCo1−xTiFe10O19
Accepted Manuscript Electromagnetic and microwave absorption properties of BaMgxCo1-xTiFe10O19 Jing Chen, Pingyuan Meng, Meiling Wang, Guanchen Zhou, Xinqing Wang, Guangliang Xu PII:
S0925-8388(16)30947-1
DOI:
10.1016/j.jallcom.2016.04.001
Reference:
JALCOM 37195
To appear in:
Journal of Alloys and Compounds
Received Date: 7 December 2015 Revised Date:
21 March 2016
Accepted Date: 1 April 2016
Please cite this article as: J. Chen, P. Meng, M. Wang, G. Zhou, X. Wang, G. Xu, Electromagnetic and microwave absorption properties of BaMgxCo1-xTiFe10O19, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.04.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Electromagnetic and microwave absorption properties of BaMgxCo1-xTiFe10O19 Jing Chena, b, Pingyuan Mengc, Meiling Wanga, b, Guanchen Zhoub, Xinqing Wanga, b,
a
RI PT
Guangliang Xub, * State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology,
School of Materials Science and Engineering, Southwest University of Science and
M AN U
b
SC
Mianyang 621010, P. R. China
Technology, Mianyang 621010, P. R. China c
Huzhou Innovation Center of Advanced Materials, Shanghai Institute of Ceramics Chinese Academy of Sciences, Huzhou 215100, P. R. China
TE D
*Corresponding author. Tel: +86-0816-6089150, Email: [email protected]
Abstract: To improve the impedance matching and then achieve a better microwave
EP
absorption performance in electromagnetic absorber, the Mg2+ was added to occupy
AC C
the sites of Co2+ in hexagonal-type ferrite BaCoTiFe10O19. BaMgxCo1-xTiFe10O19 were synthesized by a simple sol-gel combustion technique and the phase of BaMgxCo1-xTiFe10O19 was confirmed by X-ray diffraction analysis (XRD). The grain size of BaMgxCo1-xTiFe10O19 was in the range of 100-400 nm and crystal particles were refined with the augment of doped Mg2+. Based on the static magnetic measurement, the coercivity (Hc) increased and the saturation magnetization (Ms) decreased as the x increased. Moreover, it was found that BaMg0.4Co0.6TiFe10O19
ACCEPTED MANUSCRIPT possessed a maximum reflection loss of -33.7 dB with a matching thickness of 2.0 mm measured by the vector net-analyzer in the frequency of 0.5–18 GHz, which also had a bandwidth below -20 dB ranging from 11.5 GHz to 17.2 GHz. Meanwhile, the
RI PT
permeability of the prepared ferrites could be adjusted and a proper match was provided between dielectric and magnetic properties by controlling the doped content
field of the microwave absorbing materials.
SC
of Mg2+, which would be significant to the application of BaMgxCo1-xTiFe10O19 in the
M AN U
Keywords: Barium ferrite, Sol-gel combustion, Reflection loss, Broad bandwidth 1. Introduction
With the rapid development of wireless communications and high-frequency circuit devices in the gigahertz (GHz) range, electromagnetic interference (EMI)
TE D
problems have received increasing attention [1-3]. Among various types of microwave absorbing materials which have been investigated, the ferrite have been proved to be the most functional materials due to their simultaneous presence of
EP
dielectric losses and magnetic losses [4, 5].
AC C
M-type barium ferrite (BaM) can be used as a good candidate material for microwave absorption in the whole GHz region because of its high resonance frequency (about 47.6 GHz), high resistivity, low density, good chemical stability and low cost [6-9]. Moreover, it is an effective way to vary the anisotropy field by using other metal ions to replace the ferric ions (Fe3+), which can finally change the absorbing performance of BaM [6, 10]. Du and his co-worker [11] have confirmed that the magnetic resonance frequency can be moved to X band (8-12.4 GHz) by
ACCEPTED MANUSCRIPT substituting cobalt ions (Co2+) and titanium ions (Ti4+) for Fe3+ in BaM. Meng et al. [5] have demonstrated that the resonance frequency can be shifted to Ku band (12.4-18) GHz when Fe3+ are partially substituted by Ni2+ and Ti4+. In addition, the impedance
RI PT
matching between the materials and the free space is also important to the absorbing properties of ferrites, and the impedance matching is related to the µ/ɛ. For M-type barium ferrite, the value of ɛ is significantly bigger than that of µ at microwave
SC
frequencies [6, 12, 13], which could results in a bad impedance matching and a poor
M AN U
microwave attenuation in ferrites. To resolve these problems, materials possessing low permittivity, especially for the matchable permittivity, must be developed. For ionic crystals, the value of its dielectric constant is mainly determined by the electron displacement polarizability and the ionic displacement polarizability [14], by the
TE D
following equation:
(ɛ - ɛ0)/( ɛ + 2 ɛ0) = n (ɑe + ɑa)/3 ɛ0
(1)
Where n is the number of molecules per unit volume, ɑa is the ionic displacement
EP
polarizability of the materials, ɑe is the electron displacement polarizability of the
AC C
materials and ɛ0 is the vacuum dielectric constants. Equation (1) indicates that a smaller ionic displacement polarizability would be helpful to get a smaller permittivity. In oxides, the ion polarizability of Mg2+ (αMg2+ = 1.33) is smaller than that of Co2+ (αCo2+ = 1.66) and Fe3+ (αFe3+ = 2.28) [15]. Therefore, the permittiviy can decrease and then achieve a proper impedance matching through the doping of Mg2+ in BaCoTiFe10O19, which brings about a better absorbing performance.
ACCEPTED MANUSCRIPT In this work, we successfully synthesized BaMgxCo1-xTiFe10O19 powders by the sol-gel combustion method. The electromagnetic and microwave wave absorption properties of the fabricated BaMgxCo1-xTiFe10O19 were systemically investigated in
RI PT
the range of x from 0 to 0.8 at frequencies of 0.5-18 GHz. It was worth mentioning that the materials showed a good complementarity between dielectric loss and
2. Experimental
M AN U
2.1 Preparation of BaMgxCo1-xTiFe10O19 powders
SC
magnetic loss by controlling the substitution of Mg2+ ions.
Polycrystalline samples of M-type barium ferrite series (BaMgxCo1-xTiFe10O19 with x = 0-0.8 in step of 0.2) were synthesized by a conventional sol-gel combustion technique. The starting reagents, Mg(NO3)2·6H2O, Fe(NO3)3·9H2O, Ba(NO3)2, Co(NO3)2·6H2O
and
citric
acid,
are
analytical
grade
(AR,
TE D
Ti(OC4H9)4,
Sigma-Aldrich). In the solution preparation, the samples were synthesized from stoichiometric mixtures of Mg(NO3)2·6H2O, Fe(NO3)3·9H2O, Ba(NO3)2, Ti(OC4H9)4,
EP
and Co(NO3)2 ·6H2O. The mixtures were dissolved in 100 mL deionized water with
AC C
stirring. After the regents were completely dissolved, 100 mL citric acid solution (0.65 M) was added into the solution, and then the ammonia solution (AR, Sigma-Aldrich) was added by dropwise with vigorous stirring to maintain the pH value of the solution at 7. Subsequently, the neutralized solution was heated with magnetic stirring to obtain the dried gel. If keep on heating, the dried gel would burn up in a self-propagating combustion manner, and some black powders could be obtained. Finally, these powders were pre-heated at 450 °C for 4 h, and then were calcined at
ACCEPTED MANUSCRIPT 1100 °C for 4 h to obtain the BaMgxCo1-xTiFe10O19. With the increasing of the doping amount, the color of samples gradually changed from black to brown. 2.2 Preparation of BaMgxCo1-xTiFe10O19 composites
RI PT
The BaMgxCo1-xTiFe10O19 samples were dispersed in paraffin homogeneously with a sample-to-paraffin mass ratio of 85:15. Subsequently, the mixture was dissolved in xylene and ultrasonicated for 20 min, and then the mixture was kept in
SC
the oven at 55 °C to remove the solvent completely. Finally, the mixture was pressed
mm. 2.3 Measurement of properties
M AN U
into a toroidal shape with an inner diameter of 3.00 mm and an outer diameter of 7.00
The phase composition of samples were tested by X-ray diffractometer (XRD,
TE D
X'Pert PRO, PANalytical, the Netherland) using a Cu Ka source (λ = 1.5406 Å), and their components were ascertained by comparing the diffraction patterns with Joint Committee on Powder Diffraction Standards (JCPDS) cards, respectively. The
EP
size-distribution and morphology were characterized by the field emission scanning
AC C
electron microscopy (FE-SEM, Zeiss Ultra 55, Germany). Static magnetic measurement was carried out on a vibrating sample magnetometer (VSM, BKT-4500Z, China) with a maximum magnetic field of 6 kOe. The scattering parameters were recorded on an vector network analyzer (Agilent Technologies, E8363A, USA) by using the coaxial measurements in the range of 0.5-18 GHz. The relative complex permittivity (εr = εˊ - jε") and permeability (µr = µˊ - jµ") were extracted from the measured scattering parameters.
ACCEPTED MANUSCRIPT 3. Results and discussions 3.1 Phase composition and morphology of BaMgxCo1-xTiFe10O19 powders The XRD patterns of BaMgxCo1-xTiFe10O19 powders synthesized with different
RI PT
doping content of Mg2+ were shown in Fig. 1. All the diffraction peaks were very consistent with those of BaM (JCPDS Card No. 051-1879), and no second phase was detected, indicating that the incorporation of Mg2+ into BaCoTiFe10O19 did not affect
SC
its original phase [16]. However, the diffraction peaks of BaMgxCo1-xTiFe10O19
M AN U
powders had a small shift toward the side of higher 2θ with the increase of the doped Mg2+ ions. Table. 1 listed the lattice parameters of BaMgxCo1-xTiFe10O19. As shown in Table. 1, the unit cell volume of BaMgxCo1-xTiFe10O19 decreased with the increasing content of the doped Mg2+. Because the radius of Mg2+ (0.072 nm) was slightly than
that
of
Co2+
(0.0745
nm),
it
was
reasonable
that
the
TE D
smaller
BaMgxCo1-xTiFe10O19 had a smaller lattice than that of BaCoTiFe10O19, which indicated that Mg2+ might partially occupy the sites of Co2+ in BaCoTiFe10O19.
EP
The size and morphology of the synthesized BaMgxCo1-xTiFe10O19 powders (x =
AC C
0-0.8) were characterized by the FE-SEM. As shown in Fig. 2, many small BaMgxCo1-xTiFe10O19 grains grew together with a size ranging of 100-400 nm. Some agglomeration was also observed, this agglomeration might occur due to the magneto dipole interaction among the magnetic particles [17]. What’s more, it was noted that the crystal size of BaMg0.8Co0.2TiFe10O19 was obviously smaller than that of BaCoTiFe10O19, which indicated that the crystal size of BaCoTiFe10O19 could be refined via the substitution of Co2+ by Mg2+. The ionic radius of Mg2+ (0.072 nm) was
ACCEPTED MANUSCRIPT smaller than that of Co2+ (0.0745 nm), as a result, the incorporation of Mg2+ in BaCoTiFe10O19 would lead to the lattice contractions which then produced internal stress, and the stress could binder the growth of the grain [18].
RI PT
3.2 Magnetic properties of BaMgxCo1-xTiFe10O19 powders Fig. 3 showed the M-H loops of BaMgxCo1-xTiFe10O19 powders (x = 0, 0.2, 0.4, 0.6 and 0.8), which consisted of coercivity (Hc) and intrinsic saturation magnetization
SC
(Ms). As shown in Fig. 3, the Hc of BaMgxCo1-xTiFe10O19 powders was significantly
M AN U
improved with the increase of Mg2+. According to easy magnetisation directions, the hexagonal ferrites with hexagonal structure could be divided into two types, namely c-axis and c-plane anisotropy, and they correspond to the easy magnetisation along c-axis and in c-plane, respectively. In M-type hexagonal ferrite (BaFe12O19), Fe3+
TE D
occupied seven octahedral sites 12k and 2a, trigonal site 2b with spins in one direction, two octahedral sites 4f1 and two tetrahedral sites 4f2 with spins in the opposite direction. Wang et al. [3] had confirmed that the Hc of BaFe12O19 decreased with the
EP
substitution of Co2+and Ti4+ for Fe3+. This decrease in the Hc was directly related to
AC C
the intrinsic anisotropy associate with the replacement of Fe3+ ions at both 4f2 and 2b sites. Thus, these two sites contributed to a large anisotropy field. What′s more, Co2+ often contributed negative first order magnetocrystalline anisotropy constant KU1. As KU1 had a negative value, hexagonal ferrites would have c-plane anisotropy [6]. With the decrease of Co2+, the easy magnetization axis would gradually shift from c-plane to c-axis. Thus, Co2+ could have the capability to decrease the c-axis anisotropy and increase the c-plane anisotropy of the hexagonal ferrites. In this study, the increase of
ACCEPTED MANUSCRIPT the Hc of BaMgxCo1-xTiFe10O19 powders might have contributed to the enhancement of their uniaxial anisotropy along the c-axis, which was really induced by the partial substitution of Co2+ by Mg2+. Moreover, due to the lower magnetic moment of Mg2+
RI PT
(0 µB) by comparing with Co2+ (3 µB) or Fe3+ (5 µB), the Ms of BaMgxCo1-xTiFe10O19 powders gradually decreased with the augment of the substitution of Mg2+ [19]. 3.3 Complex permittivity and permeability
SC
To understand the possible microwave absorption mechanism, the complex
M AN U
permittivity and complex permeability were investigated. The real part of relative complex permittivity and permeability were the storing of energy, and the imaginary part of relative complex permittivity and permeability were the dissipation of energy [20]. The complex relative permittivity (ɛ = ɛˊ - jɛ") and the complex relative
represented in Fig. 4.
TE D
permeability (µ = µˊ - jµ") of BaMgxCo1-xTiFe10O19-paraffin composites were
Fig. 4a and 4b showed the real part (ɛˊ) and the imaginary part (ɛ") of the relative
EP
complex permittivity of BaMgxCo1-xTiFe10O19, respectively. As shown in Fig. 4a,
AC C
when Co2+ was partially substituted by Mg2+, the real part of complex permittivity (ɛˊ) decreased rapidly, and the value of ɛˊ was inversely proportional to the doping content of Mg2+. As earlier mentioned, the ion polarizability (α) in oxides of Mg2+ (αMg2+ = 1.33) was smaller than that of Co2+ (αCo2+ = 1.66) and Fe3+ (αFe3+ = 2.28). The decrease of ion polarizability could reduce the ion polarization and finally reduce the permittivity, as shown in Eq. (1) . It could be seen from the Fig. 4b, the imaginary part of complex permittivity (ɛ") of BaCoTiFe10O19 drastically rose in the frequency range
ACCEPTED MANUSCRIPT of 6.3-18 GHz, whereas the value of ɛ" decreased with the increase of x (x = 0.2-0.8) in the same frequency region. We also saw a slight augmentation of ɛ" occurred in BaMgxCo1-xTiFe10O19 when x = 0.2, which might be ascribed to the electron hopping
RI PT
that was induced by the replacement of irons [21, 22]. As earlier mentioned, the value of µ was significantly smaller than that of ɛ for ferrites at the microwave frequency range. For the impedance matching, a decrease in ɛ or an increase in µ could make the
SC
ratio closer to the unity and make the materials have a better microwave absorption
M AN U
performance [6, 23]. In this way, the incorporation of Mg2+ could effectively decrease the ɛ of BaMgxCo1-xTiFe10O19, which benefited to the impedance matching. Fig. 4c and 4d showed the real part (µˊ) and the imaginary part (µ") of the relative complex permeability of BaMgxCo1-xTiFe10O19, respectively. As shown in Fig.
TE D
4c, we could find that the µˊ curve of BaMgxCo1-xTiFe10O19 initially declined with the increase of the frequency, which could be related to the limited speed of spin and the domain wall movement (displacement/rotation) [22]. With the increase of the
EP
frequency, the value of µˊ had a slightly decline after reaching the maximum, which
AC C
was favorable for the microwave surface impedance match [24]. And as the substitution of Mg2+ increased, the maximum point of the µˊ for BaMgxCo1-xTiFe10O19 gradually shifted to higher frequency. Observing from the Fig. 4d, it could be seen that every curve of µ" had a peak and the peak moved to a higher frequency with the increasing of doping Mg2+, which had the same change trend with µˊ. It was known that the higher Hc led to a considerable shift in the resonance frequency to the higher frequencies for magnetite nanoparticles [25, 26]. In this study, the Hc of
ACCEPTED MANUSCRIPT BaMgxCo1-xTiFe10O19 increased (Fig. 3) with the increasing of x, which meant the value of magneto crystalline anisotropy of BaMgxCo1-xTiFe10O19 was bigger than that of
BaCoTiFe10O19.
As
the
magneto
crystalline
anisotropy
field
of
RI PT
BaMgxCo1-xTiFe10O19 became augmented with the increase of the doping content of Mg2+, it was easy to explain why the maximum point of the µ" of BaMgxCo1-xTiFe10O19 gradually transformed to a higher frequency. In a word, the
SC
resonance frequencies of BaMgxCo1-xTiFe10O19 could be adjustable by controlling the
M AN U
doping content of Mg2+ in the whole Ku band (12.4-18 GHz), which could be used in the fields of the electromagnetic wave absorption. 3.4 Microwave absorption properties
To study the microwave absorption properties, the reflection loss (RL) parameter
TE D
was investigated. The ability of an absorber to absorb the radiation was generally expressed in terms of RL, and the greater RL made a better absorbing effect. According to transmission line theory, the reflection loss of EM wave (normal
EP
incidence) for a microwave absorbing single layer with a metal back was calculated
AC C
by the following formula:
RL = 20log | (Zin - 1) / (Zin + 1) |
(2)
Zin = (µr /εr)1/2 tanh [ j (2 π f d /c)( µr εr)1/2]
(3)
Zin was given by:
where Zin was the normalized input impedance with respect to the impedance in free space and RL was in decibels (dB). µr and ɛr were the complex permeability and
ACCEPTED MANUSCRIPT permittivity of the composite medium, respectively, c was the velocity of light in free space, f was the frequency and d was the thickness of the absorber [27]. Fig. 5a showed the RL versus frequency in the range of 0.5-18 GHz for the
RI PT
BaMgxCo1-xTiFe10O19-paraffin composites with the thickness of 2.0 mm, calculated from Equation (2) and (3). In Fig. 5a, it was noticed that BaMg0.4Co0.6TiFe10O19 composite had a bandwidth below -10 dB (means 90% absorption) ranging from 10.5
SC
GHz to 18 GHz, which could cover the whole Ku band (12.4-18 GHz). However,
M AN U
when x was not equal to 0.4, the ferrites had a poor microwave attenuation with the thickness of 2.0 mm. As earlier mentioned, with the decrease of Co2+, the easy magnetization axis gradually shifted from c-plane to c-axis, which led to the decrease of in-plane anisotropy field Hφ and the increase of c-axis anisotropy field Ha. A big Ha
TE D
caused a small µ′, while a small Hφ led to a big µ′ [6], with the decrease of Co2+ reached a certain level, there would be a maximum of µ′. Kong et al. had also confirmed that when the thickness of the sample determined, the frequency bandwidth
EP
of the microwave absorbing materials was proportional to its static permeability (µ′)
AC C
[6]. In this study, when the thickness of BaMgxCo1-xTiFe10O19 determined, the ferrite of BaMg0.4Co0.6TiFe10O19 had the maximum bandwidth, indicating that the value of µ′ might reach its optimal value. Therefore, the enhanced wave absorption properties of BaMg0.4Co0.6TiFe10O19 composite was contributed to the optimal value of µ′, which allowed meeting the impedance matching condition [28]. The curves of RL versus frequency in the range of 0.5-18 GHz for the BaMg0.4Co0.6TiFe10O19 composite with different thicknesses were shown in Fig. 5b.
ACCEPTED MANUSCRIPT When the thickness of BaMg0.4Co0.6TiFe10O19 composite increased to 1.9 mm, two resonance peaks appeared in its RL spectrum, which was related to the domain wall motion at the lower frequency and the incoherent rotation of magnetization at the
RI PT
higher frequency [13, 29, 30]. In general, there were two different resonance mechanisms for polycrystalline ferrites under an ac field, which were called the natural resonance and domain wall resonance respectively. The natural resonance
SC
could be ascribed to the magnetization rotation and the domain wall resonance was
M AN U
closely related to the domain wall motion [31]. Moreover, the relation of the matching thickness, matching frequency and the electromagnetic parameters was also demonstrated in Fig. 5b [5], and two matching frequencies could appear when both resonances
occurred
at
a
suitable
thickness.
When
the
thickness
of
TE D
BaMg0.4Co0.6TiFe10O19 composite was 2.0 mm, the two matching frequencies appeared more clearly and the RL was enhanced. It was noticed that BaMg0.4Co0.6TiFe10O19 composite had a bandwidth below -20 dB ranging from 11.5
EP
GHz to 17.2 GHz, and it obtained a maximum RL (-33.7 dB) at f = 12.5 GHZ.
AC C
However, when the thickness of the composite was more than 2.1 mm, its RL will reduced because of the impedance mismatching [5,32]. 4. Conclusions
BaMgxCo1-xTiFe10O19 hexaferrites were prepared via the sol-gel combustion
reaction method. Mg2+ substitution could significantly modify the magnetic properties and the microstructure of the barium ferrites. The Hc of BaMgxCo1-xTiFe10O19 could be enlarged with the increase of the doped Mg2+, whereas the Ms and grain size were
ACCEPTED MANUSCRIPT inversely
proportional
to
the
doping
content
of
Mg2+.
Meanwhile,
BaMg0.4Co0.6TiFe10O19 exhibited optimum microwave absorption characteristics with a maximum reflection loss (-33.7 dB) when the thickness of composite was 2.0 mm,
RI PT
and also had a 5.7 GHz (11.5-17.2 GHz) bandwidth below -20 dB. Moreover, the permeability of the synthesized ferrites was tunable by controlling the doped content
field of the microwave absorbing materials.
M AN U
Acknowledgement
SC
of Mg2+, which would be significant to the application of BaMgxCo1-xTiFe10O19 in the
This work is supported by the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials (No. 11zxfk24). References
TE D
[1] X. Jian, X. Chen, Z. Zhou, G. Li, M. Jiang, X. Xu, J. Lu, Q. Li, Y. Wang, J. Gou, Phys. Chem. Chem. Phys. 17 (2015) 3024–3031. [2] L. Wang, Y. Huang, C. Li, J. Chen, X. Sun, Phys. Chem. Chem. Phys. 17 (2015)
EP
2228–2234.
AC C
[3] L. Wang, H.T. Yu, X.H. Ren, G.L. Xu, J. Alloys Compd. 588 (2014) 212–216. [4] X.G. Huang, J. Zhang, L.X. Wang, Q.T. Zhang, J. Alloys Compd. 540 (2012) 137–140.
[5] P.Y. Meng, K. Xiong, L. Wang, S.N. Li, Y.K. Cheng, G.L. Xu, J. Alloys Compd. 628 (2015) 75–80. [6] L.B. Kong, Z.W. Li, L. Liu, R. Huang, M. Abshinova, Z.H. Yang, C.B. Tang, P.K. Tang, C.R. Deng, S. Matitsine, Int. Mater. Rev. 58 (2013) 203–259.
ACCEPTED MANUSCRIPT [7] W.J. Zhang, Y. Bai, X. Han, L. Wang, X.F. Lu, L.J. Qiao, J. Alloys Compd. 546 (2013) 234–238. [8] F.F. Xu, L. Ma, M.Y. Gan, J.H. Tang, Z.T. Li, J.Y. Zheng, J. Zhang, S. Xie, H. Yin,
RI PT
X.Y. Shen, J.L. Hu, F. Zhang, J. Alloys Compd. 593 (2014) 24–29. [9] L.C. Li, K.Y. Chen, H. Liu, G.X. Tong, H.S. Qian, B. Hao, J. Alloys Compd. 557 (2013) 11–17.
SC
[10] C.S. Dong, X. Wang, P.H. Zhou, T. Liu, J.L. Xie, L.J. Deng, J. Magn, Magn.
M AN U
Mater. 354 (2014) 340–344.
[11] L. Du, Y.C. Du, Y. Li, J.Y. Wang, C. Wang, X.H. Wang, P. Xu, X.J. Han, J. Phys. Chem. C 114 (2010) 19600–19606.
[12] W.J. Zhang, Y. Bai, X. Han, L. Wang, X.F. Lu, L.J. Qiao, J.L. Cao, D. Guo, J.
TE D
Alloys Compd. 556 (2013) 20–25.
[13] M.K. Tehrani, A. Ghasemi, M. Moradia, R.S. Alam, J. Alloys Compd. 509 (2011) 8398–8400.
EP
[14] A.M. Portis, J. Phys. 48(1980) 259–259.
AC C
[15] R.D. Shannon, J. Appl. Phys. 73 (1993) 348–366. [16] R.D. Shannon, Acta Cryst. A 32 (1976) 751–767. [17] S.A. Khashann, E. Elnajjar, Y. Haik, J. Magn, Magn. Mater. 323 (2011) 2960–2967.
[18] M. Hashima, S. Alimuddin, S.E. Kumar, R.K. Shirsath, J. Kotnala, R. Shah, Kumar, Mater. Chem. Phys. 139 (2013) 364–374.
ACCEPTED MANUSCRIPT [19] C. Singh, S.B. Narang, I.S. Hudiara, Y. Bai, F. Tabatabaei, Mater. Res. Bull. 43 (2008) 176–184. [20] M. Zong, Y. Huang, N. Zhang, H.W. Wu, J. Alloys Compd. 644 (2015) 491–501.
RI PT
[21] P. Singh, V.K. Babbar, A. Razdan, R.K. Puri, T.C. Goel, J. Appl. Phys. 87 (2000) 4362–4366.
[22] R.S. Meena, S. Bhattachrya, R. Chatterjee, J. Magn. Magn. Mater. 322 (2010)
SC
2908–2914.
M AN U
[23] M. Jazirehpour, S.A. Seyyed Ebrahimi, J. Alloys Compd. 639 (2015) 280–288. [24] Y. Yang, B.S. Zhang, W.D. Xu, Y.B. Shi, N.S. Zhou, H.X. Lu, J. Magn. Magn. Mater. 265 (2003) 119–122.
[25] H.L. Xu, Y. Shen, H. Bi, W.F. Liang, R.B. Yang, Ferroelectrics 435 (2012)
TE D
98–103.
[26] S. Ni, S. Lin, Q. Pan, F. Yang, K. Huang, D. He, J. Phys. D: Appl. Phys. 42 (2009) 055004.
EP
[27] Z.T. Zhu, X. Sun, G.X. Li, H.R. Xue, H.Guo, X.L. Fan, X.C. Pan, J.P. He, J.
AC C
Magn, Magn. Mater. 377 (2015) 95–103. [28] P. Bhattacharya, G. Hatui, A. Mandal, C.K. Das, R. Kumar, T.C. Shami, J. Alloys Compd. 590 (2014) 331–340.
[29] F. Tabatabaie, M.H. Fathi, A. Saatchi, A. Ghasemi, J. Alloys Compd. 470 (2009) 332–335. [30] F. Tabatabaie, M.H. Fathi, A. Saatchi, A. Ghasemi, J. Alloys Compd. 474 (2009) 206–209.
ACCEPTED MANUSCRIPT [31] A. Ghasemi, V. Šepelák, X.X. Liu, A. Morisako, J. Appl. Phys. 107 (1–3) (2010) 09A734.
AC C
EP
TE D
M AN U
SC
RI PT
[32] M.S. Cao, R.R. Qin, C.J. Qiu, J. Zhu, Mater. Des. 24 (2003) 391–396.
ACCEPTED MANUSCRIPT Figure Captions Fig. 1 X-ray diffraction patterns for BaMgxCo1-xTiFe10O19 powder: (a) x = 0, (b) x = 0.2, (c) x = 0.4, (d) x = 0.6, and (e) x = 0.8
(x): (a) x = 0, (b) x = 0.4, and (c) x = 0.8
RI PT
Fig. 2 FT-SEM micrographs of BaMgxCo1-xTiFe10O19 samples with different contents
Fig. 3 Magnetic hysteresis loops of the BaMgxCo1-xTiFe10O19 ferrites for x = 0-0.8
SC
Fig. 4 Variation of dielectric constants of BaMgxCo1-xTiFe10O19 ferrites for different
M AN U
frequencies: (a) real part and (b) imaginary part of complex permittivity, (c) real part and (d) imaginary part of complex permeability.
Fig. 5 Reflection loss spectra for BaMgxCo1-xTiFe10O19 composites: (a) measured RL for different samples (x = 0-0.8) at a thickness of 2.0 mm and (b) the microwave
AC C
EP
TE D
absorption curves of BaMg0.4Co0.6TiFe10O19 sample with different thicknesses.
ACCEPTED MANUSCRIPT Table 1
Sample
Chemical formula
Calculated cell parameters
Unit cell volume V(Å3)
x=0
BaCoTiFe10O19
a (Å) 5.8980
x=0.2
BaMg0.2Co0.8TiFe10O19
5.8963
23.256
699.85
x=0.4
BaMg0.4Co0.6TiFe10O19
5.8960
23.241
699.78
x=0.6
BaMg0.6Co0.4TiFe10O19
5.8952
23.228
699.09
x=0.8
BaMg0.8Co0.2TiFe10O19
5.8950
23.219
699.02
SC M AN U TE D EP AC C
699.98
RI PT
c (Å) 23.238
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT Highlights The Mg2+ ions were first employed to occupy the place of Co2+ ions in BaCoTiFe10O19.
RI PT
The grains were refined as Co substitution by Mg in ferrite. The peaks of complex permeability shift to high frequency with Mg2+ substituted. The coercivity increased and saturation magnetization slightly decreased.
AC C
EP
TE D
M AN U
SC
Substitution of Mg2+ enhanced microwave absorption and broadened bandwidth.
S0925-8388(16)30947-1
DOI:
10.1016/j.jallcom.2016.04.001
Reference:
JALCOM 37195
To appear in:
Journal of Alloys and Compounds
Received Date: 7 December 2015 Revised Date:
21 March 2016
Accepted Date: 1 April 2016
Please cite this article as: J. Chen, P. Meng, M. Wang, G. Zhou, X. Wang, G. Xu, Electromagnetic and microwave absorption properties of BaMgxCo1-xTiFe10O19, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.04.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Electromagnetic and microwave absorption properties of BaMgxCo1-xTiFe10O19 Jing Chena, b, Pingyuan Mengc, Meiling Wanga, b, Guanchen Zhoub, Xinqing Wanga, b,
a
RI PT
Guangliang Xub, * State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology,
School of Materials Science and Engineering, Southwest University of Science and
M AN U
b
SC
Mianyang 621010, P. R. China
Technology, Mianyang 621010, P. R. China c
Huzhou Innovation Center of Advanced Materials, Shanghai Institute of Ceramics Chinese Academy of Sciences, Huzhou 215100, P. R. China
TE D
*Corresponding author. Tel: +86-0816-6089150, Email: [email protected]
Abstract: To improve the impedance matching and then achieve a better microwave
EP
absorption performance in electromagnetic absorber, the Mg2+ was added to occupy
AC C
the sites of Co2+ in hexagonal-type ferrite BaCoTiFe10O19. BaMgxCo1-xTiFe10O19 were synthesized by a simple sol-gel combustion technique and the phase of BaMgxCo1-xTiFe10O19 was confirmed by X-ray diffraction analysis (XRD). The grain size of BaMgxCo1-xTiFe10O19 was in the range of 100-400 nm and crystal particles were refined with the augment of doped Mg2+. Based on the static magnetic measurement, the coercivity (Hc) increased and the saturation magnetization (Ms) decreased as the x increased. Moreover, it was found that BaMg0.4Co0.6TiFe10O19
ACCEPTED MANUSCRIPT possessed a maximum reflection loss of -33.7 dB with a matching thickness of 2.0 mm measured by the vector net-analyzer in the frequency of 0.5–18 GHz, which also had a bandwidth below -20 dB ranging from 11.5 GHz to 17.2 GHz. Meanwhile, the
RI PT
permeability of the prepared ferrites could be adjusted and a proper match was provided between dielectric and magnetic properties by controlling the doped content
field of the microwave absorbing materials.
SC
of Mg2+, which would be significant to the application of BaMgxCo1-xTiFe10O19 in the
M AN U
Keywords: Barium ferrite, Sol-gel combustion, Reflection loss, Broad bandwidth 1. Introduction
With the rapid development of wireless communications and high-frequency circuit devices in the gigahertz (GHz) range, electromagnetic interference (EMI)
TE D
problems have received increasing attention [1-3]. Among various types of microwave absorbing materials which have been investigated, the ferrite have been proved to be the most functional materials due to their simultaneous presence of
EP
dielectric losses and magnetic losses [4, 5].
AC C
M-type barium ferrite (BaM) can be used as a good candidate material for microwave absorption in the whole GHz region because of its high resonance frequency (about 47.6 GHz), high resistivity, low density, good chemical stability and low cost [6-9]. Moreover, it is an effective way to vary the anisotropy field by using other metal ions to replace the ferric ions (Fe3+), which can finally change the absorbing performance of BaM [6, 10]. Du and his co-worker [11] have confirmed that the magnetic resonance frequency can be moved to X band (8-12.4 GHz) by
ACCEPTED MANUSCRIPT substituting cobalt ions (Co2+) and titanium ions (Ti4+) for Fe3+ in BaM. Meng et al. [5] have demonstrated that the resonance frequency can be shifted to Ku band (12.4-18) GHz when Fe3+ are partially substituted by Ni2+ and Ti4+. In addition, the impedance
RI PT
matching between the materials and the free space is also important to the absorbing properties of ferrites, and the impedance matching is related to the µ/ɛ. For M-type barium ferrite, the value of ɛ is significantly bigger than that of µ at microwave
SC
frequencies [6, 12, 13], which could results in a bad impedance matching and a poor
M AN U
microwave attenuation in ferrites. To resolve these problems, materials possessing low permittivity, especially for the matchable permittivity, must be developed. For ionic crystals, the value of its dielectric constant is mainly determined by the electron displacement polarizability and the ionic displacement polarizability [14], by the
TE D
following equation:
(ɛ - ɛ0)/( ɛ + 2 ɛ0) = n (ɑe + ɑa)/3 ɛ0
(1)
Where n is the number of molecules per unit volume, ɑa is the ionic displacement
EP
polarizability of the materials, ɑe is the electron displacement polarizability of the
AC C
materials and ɛ0 is the vacuum dielectric constants. Equation (1) indicates that a smaller ionic displacement polarizability would be helpful to get a smaller permittivity. In oxides, the ion polarizability of Mg2+ (αMg2+ = 1.33) is smaller than that of Co2+ (αCo2+ = 1.66) and Fe3+ (αFe3+ = 2.28) [15]. Therefore, the permittiviy can decrease and then achieve a proper impedance matching through the doping of Mg2+ in BaCoTiFe10O19, which brings about a better absorbing performance.
ACCEPTED MANUSCRIPT In this work, we successfully synthesized BaMgxCo1-xTiFe10O19 powders by the sol-gel combustion method. The electromagnetic and microwave wave absorption properties of the fabricated BaMgxCo1-xTiFe10O19 were systemically investigated in
RI PT
the range of x from 0 to 0.8 at frequencies of 0.5-18 GHz. It was worth mentioning that the materials showed a good complementarity between dielectric loss and
2. Experimental
M AN U
2.1 Preparation of BaMgxCo1-xTiFe10O19 powders
SC
magnetic loss by controlling the substitution of Mg2+ ions.
Polycrystalline samples of M-type barium ferrite series (BaMgxCo1-xTiFe10O19 with x = 0-0.8 in step of 0.2) were synthesized by a conventional sol-gel combustion technique. The starting reagents, Mg(NO3)2·6H2O, Fe(NO3)3·9H2O, Ba(NO3)2, Co(NO3)2·6H2O
and
citric
acid,
are
analytical
grade
(AR,
TE D
Ti(OC4H9)4,
Sigma-Aldrich). In the solution preparation, the samples were synthesized from stoichiometric mixtures of Mg(NO3)2·6H2O, Fe(NO3)3·9H2O, Ba(NO3)2, Ti(OC4H9)4,
EP
and Co(NO3)2 ·6H2O. The mixtures were dissolved in 100 mL deionized water with
AC C
stirring. After the regents were completely dissolved, 100 mL citric acid solution (0.65 M) was added into the solution, and then the ammonia solution (AR, Sigma-Aldrich) was added by dropwise with vigorous stirring to maintain the pH value of the solution at 7. Subsequently, the neutralized solution was heated with magnetic stirring to obtain the dried gel. If keep on heating, the dried gel would burn up in a self-propagating combustion manner, and some black powders could be obtained. Finally, these powders were pre-heated at 450 °C for 4 h, and then were calcined at
ACCEPTED MANUSCRIPT 1100 °C for 4 h to obtain the BaMgxCo1-xTiFe10O19. With the increasing of the doping amount, the color of samples gradually changed from black to brown. 2.2 Preparation of BaMgxCo1-xTiFe10O19 composites
RI PT
The BaMgxCo1-xTiFe10O19 samples were dispersed in paraffin homogeneously with a sample-to-paraffin mass ratio of 85:15. Subsequently, the mixture was dissolved in xylene and ultrasonicated for 20 min, and then the mixture was kept in
SC
the oven at 55 °C to remove the solvent completely. Finally, the mixture was pressed
mm. 2.3 Measurement of properties
M AN U
into a toroidal shape with an inner diameter of 3.00 mm and an outer diameter of 7.00
The phase composition of samples were tested by X-ray diffractometer (XRD,
TE D
X'Pert PRO, PANalytical, the Netherland) using a Cu Ka source (λ = 1.5406 Å), and their components were ascertained by comparing the diffraction patterns with Joint Committee on Powder Diffraction Standards (JCPDS) cards, respectively. The
EP
size-distribution and morphology were characterized by the field emission scanning
AC C
electron microscopy (FE-SEM, Zeiss Ultra 55, Germany). Static magnetic measurement was carried out on a vibrating sample magnetometer (VSM, BKT-4500Z, China) with a maximum magnetic field of 6 kOe. The scattering parameters were recorded on an vector network analyzer (Agilent Technologies, E8363A, USA) by using the coaxial measurements in the range of 0.5-18 GHz. The relative complex permittivity (εr = εˊ - jε") and permeability (µr = µˊ - jµ") were extracted from the measured scattering parameters.
ACCEPTED MANUSCRIPT 3. Results and discussions 3.1 Phase composition and morphology of BaMgxCo1-xTiFe10O19 powders The XRD patterns of BaMgxCo1-xTiFe10O19 powders synthesized with different
RI PT
doping content of Mg2+ were shown in Fig. 1. All the diffraction peaks were very consistent with those of BaM (JCPDS Card No. 051-1879), and no second phase was detected, indicating that the incorporation of Mg2+ into BaCoTiFe10O19 did not affect
SC
its original phase [16]. However, the diffraction peaks of BaMgxCo1-xTiFe10O19
M AN U
powders had a small shift toward the side of higher 2θ with the increase of the doped Mg2+ ions. Table. 1 listed the lattice parameters of BaMgxCo1-xTiFe10O19. As shown in Table. 1, the unit cell volume of BaMgxCo1-xTiFe10O19 decreased with the increasing content of the doped Mg2+. Because the radius of Mg2+ (0.072 nm) was slightly than
that
of
Co2+
(0.0745
nm),
it
was
reasonable
that
the
TE D
smaller
BaMgxCo1-xTiFe10O19 had a smaller lattice than that of BaCoTiFe10O19, which indicated that Mg2+ might partially occupy the sites of Co2+ in BaCoTiFe10O19.
EP
The size and morphology of the synthesized BaMgxCo1-xTiFe10O19 powders (x =
AC C
0-0.8) were characterized by the FE-SEM. As shown in Fig. 2, many small BaMgxCo1-xTiFe10O19 grains grew together with a size ranging of 100-400 nm. Some agglomeration was also observed, this agglomeration might occur due to the magneto dipole interaction among the magnetic particles [17]. What’s more, it was noted that the crystal size of BaMg0.8Co0.2TiFe10O19 was obviously smaller than that of BaCoTiFe10O19, which indicated that the crystal size of BaCoTiFe10O19 could be refined via the substitution of Co2+ by Mg2+. The ionic radius of Mg2+ (0.072 nm) was
ACCEPTED MANUSCRIPT smaller than that of Co2+ (0.0745 nm), as a result, the incorporation of Mg2+ in BaCoTiFe10O19 would lead to the lattice contractions which then produced internal stress, and the stress could binder the growth of the grain [18].
RI PT
3.2 Magnetic properties of BaMgxCo1-xTiFe10O19 powders Fig. 3 showed the M-H loops of BaMgxCo1-xTiFe10O19 powders (x = 0, 0.2, 0.4, 0.6 and 0.8), which consisted of coercivity (Hc) and intrinsic saturation magnetization
SC
(Ms). As shown in Fig. 3, the Hc of BaMgxCo1-xTiFe10O19 powders was significantly
M AN U
improved with the increase of Mg2+. According to easy magnetisation directions, the hexagonal ferrites with hexagonal structure could be divided into two types, namely c-axis and c-plane anisotropy, and they correspond to the easy magnetisation along c-axis and in c-plane, respectively. In M-type hexagonal ferrite (BaFe12O19), Fe3+
TE D
occupied seven octahedral sites 12k and 2a, trigonal site 2b with spins in one direction, two octahedral sites 4f1 and two tetrahedral sites 4f2 with spins in the opposite direction. Wang et al. [3] had confirmed that the Hc of BaFe12O19 decreased with the
EP
substitution of Co2+and Ti4+ for Fe3+. This decrease in the Hc was directly related to
AC C
the intrinsic anisotropy associate with the replacement of Fe3+ ions at both 4f2 and 2b sites. Thus, these two sites contributed to a large anisotropy field. What′s more, Co2+ often contributed negative first order magnetocrystalline anisotropy constant KU1. As KU1 had a negative value, hexagonal ferrites would have c-plane anisotropy [6]. With the decrease of Co2+, the easy magnetization axis would gradually shift from c-plane to c-axis. Thus, Co2+ could have the capability to decrease the c-axis anisotropy and increase the c-plane anisotropy of the hexagonal ferrites. In this study, the increase of
ACCEPTED MANUSCRIPT the Hc of BaMgxCo1-xTiFe10O19 powders might have contributed to the enhancement of their uniaxial anisotropy along the c-axis, which was really induced by the partial substitution of Co2+ by Mg2+. Moreover, due to the lower magnetic moment of Mg2+
RI PT
(0 µB) by comparing with Co2+ (3 µB) or Fe3+ (5 µB), the Ms of BaMgxCo1-xTiFe10O19 powders gradually decreased with the augment of the substitution of Mg2+ [19]. 3.3 Complex permittivity and permeability
SC
To understand the possible microwave absorption mechanism, the complex
M AN U
permittivity and complex permeability were investigated. The real part of relative complex permittivity and permeability were the storing of energy, and the imaginary part of relative complex permittivity and permeability were the dissipation of energy [20]. The complex relative permittivity (ɛ = ɛˊ - jɛ") and the complex relative
represented in Fig. 4.
TE D
permeability (µ = µˊ - jµ") of BaMgxCo1-xTiFe10O19-paraffin composites were
Fig. 4a and 4b showed the real part (ɛˊ) and the imaginary part (ɛ") of the relative
EP
complex permittivity of BaMgxCo1-xTiFe10O19, respectively. As shown in Fig. 4a,
AC C
when Co2+ was partially substituted by Mg2+, the real part of complex permittivity (ɛˊ) decreased rapidly, and the value of ɛˊ was inversely proportional to the doping content of Mg2+. As earlier mentioned, the ion polarizability (α) in oxides of Mg2+ (αMg2+ = 1.33) was smaller than that of Co2+ (αCo2+ = 1.66) and Fe3+ (αFe3+ = 2.28). The decrease of ion polarizability could reduce the ion polarization and finally reduce the permittivity, as shown in Eq. (1) . It could be seen from the Fig. 4b, the imaginary part of complex permittivity (ɛ") of BaCoTiFe10O19 drastically rose in the frequency range
ACCEPTED MANUSCRIPT of 6.3-18 GHz, whereas the value of ɛ" decreased with the increase of x (x = 0.2-0.8) in the same frequency region. We also saw a slight augmentation of ɛ" occurred in BaMgxCo1-xTiFe10O19 when x = 0.2, which might be ascribed to the electron hopping
RI PT
that was induced by the replacement of irons [21, 22]. As earlier mentioned, the value of µ was significantly smaller than that of ɛ for ferrites at the microwave frequency range. For the impedance matching, a decrease in ɛ or an increase in µ could make the
SC
ratio closer to the unity and make the materials have a better microwave absorption
M AN U
performance [6, 23]. In this way, the incorporation of Mg2+ could effectively decrease the ɛ of BaMgxCo1-xTiFe10O19, which benefited to the impedance matching. Fig. 4c and 4d showed the real part (µˊ) and the imaginary part (µ") of the relative complex permeability of BaMgxCo1-xTiFe10O19, respectively. As shown in Fig.
TE D
4c, we could find that the µˊ curve of BaMgxCo1-xTiFe10O19 initially declined with the increase of the frequency, which could be related to the limited speed of spin and the domain wall movement (displacement/rotation) [22]. With the increase of the
EP
frequency, the value of µˊ had a slightly decline after reaching the maximum, which
AC C
was favorable for the microwave surface impedance match [24]. And as the substitution of Mg2+ increased, the maximum point of the µˊ for BaMgxCo1-xTiFe10O19 gradually shifted to higher frequency. Observing from the Fig. 4d, it could be seen that every curve of µ" had a peak and the peak moved to a higher frequency with the increasing of doping Mg2+, which had the same change trend with µˊ. It was known that the higher Hc led to a considerable shift in the resonance frequency to the higher frequencies for magnetite nanoparticles [25, 26]. In this study, the Hc of
ACCEPTED MANUSCRIPT BaMgxCo1-xTiFe10O19 increased (Fig. 3) with the increasing of x, which meant the value of magneto crystalline anisotropy of BaMgxCo1-xTiFe10O19 was bigger than that of
BaCoTiFe10O19.
As
the
magneto
crystalline
anisotropy
field
of
RI PT
BaMgxCo1-xTiFe10O19 became augmented with the increase of the doping content of Mg2+, it was easy to explain why the maximum point of the µ" of BaMgxCo1-xTiFe10O19 gradually transformed to a higher frequency. In a word, the
SC
resonance frequencies of BaMgxCo1-xTiFe10O19 could be adjustable by controlling the
M AN U
doping content of Mg2+ in the whole Ku band (12.4-18 GHz), which could be used in the fields of the electromagnetic wave absorption. 3.4 Microwave absorption properties
To study the microwave absorption properties, the reflection loss (RL) parameter
TE D
was investigated. The ability of an absorber to absorb the radiation was generally expressed in terms of RL, and the greater RL made a better absorbing effect. According to transmission line theory, the reflection loss of EM wave (normal
EP
incidence) for a microwave absorbing single layer with a metal back was calculated
AC C
by the following formula:
RL = 20log | (Zin - 1) / (Zin + 1) |
(2)
Zin = (µr /εr)1/2 tanh [ j (2 π f d /c)( µr εr)1/2]
(3)
Zin was given by:
where Zin was the normalized input impedance with respect to the impedance in free space and RL was in decibels (dB). µr and ɛr were the complex permeability and
ACCEPTED MANUSCRIPT permittivity of the composite medium, respectively, c was the velocity of light in free space, f was the frequency and d was the thickness of the absorber [27]. Fig. 5a showed the RL versus frequency in the range of 0.5-18 GHz for the
RI PT
BaMgxCo1-xTiFe10O19-paraffin composites with the thickness of 2.0 mm, calculated from Equation (2) and (3). In Fig. 5a, it was noticed that BaMg0.4Co0.6TiFe10O19 composite had a bandwidth below -10 dB (means 90% absorption) ranging from 10.5
SC
GHz to 18 GHz, which could cover the whole Ku band (12.4-18 GHz). However,
M AN U
when x was not equal to 0.4, the ferrites had a poor microwave attenuation with the thickness of 2.0 mm. As earlier mentioned, with the decrease of Co2+, the easy magnetization axis gradually shifted from c-plane to c-axis, which led to the decrease of in-plane anisotropy field Hφ and the increase of c-axis anisotropy field Ha. A big Ha
TE D
caused a small µ′, while a small Hφ led to a big µ′ [6], with the decrease of Co2+ reached a certain level, there would be a maximum of µ′. Kong et al. had also confirmed that when the thickness of the sample determined, the frequency bandwidth
EP
of the microwave absorbing materials was proportional to its static permeability (µ′)
AC C
[6]. In this study, when the thickness of BaMgxCo1-xTiFe10O19 determined, the ferrite of BaMg0.4Co0.6TiFe10O19 had the maximum bandwidth, indicating that the value of µ′ might reach its optimal value. Therefore, the enhanced wave absorption properties of BaMg0.4Co0.6TiFe10O19 composite was contributed to the optimal value of µ′, which allowed meeting the impedance matching condition [28]. The curves of RL versus frequency in the range of 0.5-18 GHz for the BaMg0.4Co0.6TiFe10O19 composite with different thicknesses were shown in Fig. 5b.
ACCEPTED MANUSCRIPT When the thickness of BaMg0.4Co0.6TiFe10O19 composite increased to 1.9 mm, two resonance peaks appeared in its RL spectrum, which was related to the domain wall motion at the lower frequency and the incoherent rotation of magnetization at the
RI PT
higher frequency [13, 29, 30]. In general, there were two different resonance mechanisms for polycrystalline ferrites under an ac field, which were called the natural resonance and domain wall resonance respectively. The natural resonance
SC
could be ascribed to the magnetization rotation and the domain wall resonance was
M AN U
closely related to the domain wall motion [31]. Moreover, the relation of the matching thickness, matching frequency and the electromagnetic parameters was also demonstrated in Fig. 5b [5], and two matching frequencies could appear when both resonances
occurred
at
a
suitable
thickness.
When
the
thickness
of
TE D
BaMg0.4Co0.6TiFe10O19 composite was 2.0 mm, the two matching frequencies appeared more clearly and the RL was enhanced. It was noticed that BaMg0.4Co0.6TiFe10O19 composite had a bandwidth below -20 dB ranging from 11.5
EP
GHz to 17.2 GHz, and it obtained a maximum RL (-33.7 dB) at f = 12.5 GHZ.
AC C
However, when the thickness of the composite was more than 2.1 mm, its RL will reduced because of the impedance mismatching [5,32]. 4. Conclusions
BaMgxCo1-xTiFe10O19 hexaferrites were prepared via the sol-gel combustion
reaction method. Mg2+ substitution could significantly modify the magnetic properties and the microstructure of the barium ferrites. The Hc of BaMgxCo1-xTiFe10O19 could be enlarged with the increase of the doped Mg2+, whereas the Ms and grain size were
ACCEPTED MANUSCRIPT inversely
proportional
to
the
doping
content
of
Mg2+.
Meanwhile,
BaMg0.4Co0.6TiFe10O19 exhibited optimum microwave absorption characteristics with a maximum reflection loss (-33.7 dB) when the thickness of composite was 2.0 mm,
RI PT
and also had a 5.7 GHz (11.5-17.2 GHz) bandwidth below -20 dB. Moreover, the permeability of the synthesized ferrites was tunable by controlling the doped content
field of the microwave absorbing materials.
M AN U
Acknowledgement
SC
of Mg2+, which would be significant to the application of BaMgxCo1-xTiFe10O19 in the
This work is supported by the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials (No. 11zxfk24). References
TE D
[1] X. Jian, X. Chen, Z. Zhou, G. Li, M. Jiang, X. Xu, J. Lu, Q. Li, Y. Wang, J. Gou, Phys. Chem. Chem. Phys. 17 (2015) 3024–3031. [2] L. Wang, Y. Huang, C. Li, J. Chen, X. Sun, Phys. Chem. Chem. Phys. 17 (2015)
EP
2228–2234.
AC C
[3] L. Wang, H.T. Yu, X.H. Ren, G.L. Xu, J. Alloys Compd. 588 (2014) 212–216. [4] X.G. Huang, J. Zhang, L.X. Wang, Q.T. Zhang, J. Alloys Compd. 540 (2012) 137–140.
[5] P.Y. Meng, K. Xiong, L. Wang, S.N. Li, Y.K. Cheng, G.L. Xu, J. Alloys Compd. 628 (2015) 75–80. [6] L.B. Kong, Z.W. Li, L. Liu, R. Huang, M. Abshinova, Z.H. Yang, C.B. Tang, P.K. Tang, C.R. Deng, S. Matitsine, Int. Mater. Rev. 58 (2013) 203–259.
ACCEPTED MANUSCRIPT [7] W.J. Zhang, Y. Bai, X. Han, L. Wang, X.F. Lu, L.J. Qiao, J. Alloys Compd. 546 (2013) 234–238. [8] F.F. Xu, L. Ma, M.Y. Gan, J.H. Tang, Z.T. Li, J.Y. Zheng, J. Zhang, S. Xie, H. Yin,
RI PT
X.Y. Shen, J.L. Hu, F. Zhang, J. Alloys Compd. 593 (2014) 24–29. [9] L.C. Li, K.Y. Chen, H. Liu, G.X. Tong, H.S. Qian, B. Hao, J. Alloys Compd. 557 (2013) 11–17.
SC
[10] C.S. Dong, X. Wang, P.H. Zhou, T. Liu, J.L. Xie, L.J. Deng, J. Magn, Magn.
M AN U
Mater. 354 (2014) 340–344.
[11] L. Du, Y.C. Du, Y. Li, J.Y. Wang, C. Wang, X.H. Wang, P. Xu, X.J. Han, J. Phys. Chem. C 114 (2010) 19600–19606.
[12] W.J. Zhang, Y. Bai, X. Han, L. Wang, X.F. Lu, L.J. Qiao, J.L. Cao, D. Guo, J.
TE D
Alloys Compd. 556 (2013) 20–25.
[13] M.K. Tehrani, A. Ghasemi, M. Moradia, R.S. Alam, J. Alloys Compd. 509 (2011) 8398–8400.
EP
[14] A.M. Portis, J. Phys. 48(1980) 259–259.
AC C
[15] R.D. Shannon, J. Appl. Phys. 73 (1993) 348–366. [16] R.D. Shannon, Acta Cryst. A 32 (1976) 751–767. [17] S.A. Khashann, E. Elnajjar, Y. Haik, J. Magn, Magn. Mater. 323 (2011) 2960–2967.
[18] M. Hashima, S. Alimuddin, S.E. Kumar, R.K. Shirsath, J. Kotnala, R. Shah, Kumar, Mater. Chem. Phys. 139 (2013) 364–374.
ACCEPTED MANUSCRIPT [19] C. Singh, S.B. Narang, I.S. Hudiara, Y. Bai, F. Tabatabaei, Mater. Res. Bull. 43 (2008) 176–184. [20] M. Zong, Y. Huang, N. Zhang, H.W. Wu, J. Alloys Compd. 644 (2015) 491–501.
RI PT
[21] P. Singh, V.K. Babbar, A. Razdan, R.K. Puri, T.C. Goel, J. Appl. Phys. 87 (2000) 4362–4366.
[22] R.S. Meena, S. Bhattachrya, R. Chatterjee, J. Magn. Magn. Mater. 322 (2010)
SC
2908–2914.
M AN U
[23] M. Jazirehpour, S.A. Seyyed Ebrahimi, J. Alloys Compd. 639 (2015) 280–288. [24] Y. Yang, B.S. Zhang, W.D. Xu, Y.B. Shi, N.S. Zhou, H.X. Lu, J. Magn. Magn. Mater. 265 (2003) 119–122.
[25] H.L. Xu, Y. Shen, H. Bi, W.F. Liang, R.B. Yang, Ferroelectrics 435 (2012)
TE D
98–103.
[26] S. Ni, S. Lin, Q. Pan, F. Yang, K. Huang, D. He, J. Phys. D: Appl. Phys. 42 (2009) 055004.
EP
[27] Z.T. Zhu, X. Sun, G.X. Li, H.R. Xue, H.Guo, X.L. Fan, X.C. Pan, J.P. He, J.
AC C
Magn, Magn. Mater. 377 (2015) 95–103. [28] P. Bhattacharya, G. Hatui, A. Mandal, C.K. Das, R. Kumar, T.C. Shami, J. Alloys Compd. 590 (2014) 331–340.
[29] F. Tabatabaie, M.H. Fathi, A. Saatchi, A. Ghasemi, J. Alloys Compd. 470 (2009) 332–335. [30] F. Tabatabaie, M.H. Fathi, A. Saatchi, A. Ghasemi, J. Alloys Compd. 474 (2009) 206–209.
ACCEPTED MANUSCRIPT [31] A. Ghasemi, V. Šepelák, X.X. Liu, A. Morisako, J. Appl. Phys. 107 (1–3) (2010) 09A734.
AC C
EP
TE D
M AN U
SC
RI PT
[32] M.S. Cao, R.R. Qin, C.J. Qiu, J. Zhu, Mater. Des. 24 (2003) 391–396.
ACCEPTED MANUSCRIPT Figure Captions Fig. 1 X-ray diffraction patterns for BaMgxCo1-xTiFe10O19 powder: (a) x = 0, (b) x = 0.2, (c) x = 0.4, (d) x = 0.6, and (e) x = 0.8
(x): (a) x = 0, (b) x = 0.4, and (c) x = 0.8
RI PT
Fig. 2 FT-SEM micrographs of BaMgxCo1-xTiFe10O19 samples with different contents
Fig. 3 Magnetic hysteresis loops of the BaMgxCo1-xTiFe10O19 ferrites for x = 0-0.8
SC
Fig. 4 Variation of dielectric constants of BaMgxCo1-xTiFe10O19 ferrites for different
M AN U
frequencies: (a) real part and (b) imaginary part of complex permittivity, (c) real part and (d) imaginary part of complex permeability.
Fig. 5 Reflection loss spectra for BaMgxCo1-xTiFe10O19 composites: (a) measured RL for different samples (x = 0-0.8) at a thickness of 2.0 mm and (b) the microwave
AC C
EP
TE D
absorption curves of BaMg0.4Co0.6TiFe10O19 sample with different thicknesses.
ACCEPTED MANUSCRIPT Table 1
Sample
Chemical formula
Calculated cell parameters
Unit cell volume V(Å3)
x=0
BaCoTiFe10O19
a (Å) 5.8980
x=0.2
BaMg0.2Co0.8TiFe10O19
5.8963
23.256
699.85
x=0.4
BaMg0.4Co0.6TiFe10O19
5.8960
23.241
699.78
x=0.6
BaMg0.6Co0.4TiFe10O19
5.8952
23.228
699.09
x=0.8
BaMg0.8Co0.2TiFe10O19
5.8950
23.219
699.02
SC M AN U TE D EP AC C
699.98
RI PT
c (Å) 23.238
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT Highlights The Mg2+ ions were first employed to occupy the place of Co2+ ions in BaCoTiFe10O19.
RI PT
The grains were refined as Co substitution by Mg in ferrite. The peaks of complex permeability shift to high frequency with Mg2+ substituted. The coercivity increased and saturation magnetization slightly decreased.
AC C
EP
TE D
M AN U
SC
Substitution of Mg2+ enhanced microwave absorption and broadened bandwidth.